Testing solution models for phase equilibrium (forward) modeling of partial melting experiments

Abstract

This study compares four sets of solution (or activity-composition) models using two internally consistent thermodynamic datasets for calculating isochemical phase diagram sections of six partial melting experiments covering a wide range of metasedimentary bulk compositions. Compared parameters are: (1) biotite-breakdown temperatures; (2) parageneses of Fe–Mg phases and Ti-oxides; (3) proportion of biotite, garnet, liquid and plagioclase; (4) Mg# of biotite, garnet and liquid and the anorthite content of plagioclase. Results reveal significant differences between sets that are mainly related to the construction of the biotite solution, with the model of Tajcmanova et al. (2009) yielding better results for the majority of investigated parameters. Owing to the success of the investigated set of solution models at reproducing the proxy that constitutes partial melting experiments, but also at reproducing natural observations as published elsewhere, it is suggested that this biotite model should be used in the Ti–Mn–Na–Ca–K–Fe–Mg–Al–Si–H–O system for phase equilibrium (forward) modeling of metasediments.